The present invention relates to a scroll fluid machine, and particularly to a scroll fluid machine, such as a scroll vacuum pump or a scroll pressurizing machine, in which a fixed wrap of a fixed scroll in a housing is engaged with an orbiting wrap of an orbiting scroll rotatably connected to an eccentric axial portion of a driving shaft, the orbiting scroll being revolved at a certain eccentricity by the driving shaft, thereby compressing a gas sucked from the circumference or the center of the housing as it moves toward the center or circumference and being discharged.
Such a scroll fluid machine is known among persons skilled in the art.
A scroll fluid machine runs for a long time, so that temperatures of a driving shaft, an eccentric axial portion of the driving shaft, bearings and packings rise to result in damage in the bearings and packings or in leak of lubricating oil. Hence it makes the machine impossible to use.
To increase durability of the scroll fluid machine, it is necessary to avoid excessive high temperature on the eccentric axial portion of the driving shaft during long-time operation.
To comply with such requirements, the following measures are taken and known among persons skilled in the art.
(1) Low or room temperature air or nitrogen is introduced into a compressing portion of a scroll fluid machine to dilute toxicity in the compressing portion.
(2) A gas-guiding bore is axially formed in a driving shaft, and a low or room temperature air or nitrogen is discharged through the gas-guiding bore. After it passes through the bearing, it is introduced into the compressing portion, which is cooled by the air or nitrogen which is discharged.
(3) An eccentric axial portion of the driving shaft is formed as hollow into which low or room temperature air is introduced to cool the eccentric axial portion.
However there are disadvantages as below in the foregoing measures.
In order to introduce low or room temperature air or nitrogen into the compressing portion, it is necessary to provide introducing paths and outside supply means. Thus, the structure becomes complicate and makes its size larger to result in high cost.
A gas-guiding bore is axially formed in a driving shaft, and low or room temperature air or nitrogen is discharged through the gas-guiding bore by centrifugal force caused by rotation of the driving shaft to cool bearings. In this device, when the driving shaft stops, a toxic or foreign-substance-containing gas in a compressing portion runs back and is discharged to atmosphere through the gas-guiding bore, thereby causing contamination in atmosphere.